1. Field of the Invention
This invention relates to a catadioptric lens barrel which can be attached to an optical projection unit, such as a projection exposure apparatus used to manufacture semiconductor wafers. More particularly, the present invention relates to a catadioptric lens barrel structure including its support structure, the lens barrel structure comprising a plurality of lens barrels aligned in parallel, and at least one transverse lens barrel connecting the plurality of lens barrels.
2. Description of the Related Art
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end of the lens barrel to the other. The lens barrel may include a sturdy threaded body and durable metal retaining rings, often referred to as xe2x80x9csub-barrels,xe2x80x9d to carry a series of lens holders, commonly referred to as xe2x80x9ccells.xe2x80x9d Another type of lens barrel is known as a catadioptric lens barrel. A catadioptric lens barrel contains not only refractive elements, such as lenses, but also reflective elements, such as mirrors.
Both of these lens barrel designs are used in conventional optical systems. For example, optical projection units often have a lens barrel and may be used in a projection exposure apparatus for production of semiconductor wafers. The projection exposure apparatus includes a template positioned near an entrance end of the lens barrel and a semiconductor wafer positioned near an exit end. The projection exposure apparatus shines light through the template, photographically reduces a pattern on the template, and sequentially transfers the pattern, through the lens barrel, onto a predetermined area on the semiconductor wafer. The template may be of a form such as a reticle or a mask. The semiconductor wafer is a silicon wafer with a photo-sensitive coating for making semiconductor devices, such as microprocessor or memory chips.
A catadioptric lens barrel system using two or more lens barrels, arranged in parallel, offers benefits not found in conventional single barrel systems. The parallelism of the lens barrels reduces the overall height of the lens barrel, but increases the overall width. Reduced height is important for many reasons, such as for ease of transport. This type of catadioptric lens barrel design, however, poses several problems. First, keeping proper alignment of a plurality of lens barrels can be difficult. Second, the focus depth of the projection system changes as temperature changes. Coefficients of thermal expansion of the lens barrels, including their internal components, and the indices of refraction of all lens materials vary with temperature. Errors related to these factors collectively alter the focusing properties of the optical system. Third, the lens barrel structure tends to be more sensitive to movement or vibration than conventional single barrel designs.
In light of the foregoing, there is a need for a catadioptric lens barrel structure that holds the lens barrels stabily and accurately, and minimizes distortion errors due to temperature changes, vibrational, or other external forces, so that the resulting image remains focused as it is transferred and reduced from the reticle to the semiconductor wafer.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, one aspect of the invention is directed to a lens barrel structure. The lens barrel structure may be used, for example, in a projection exposure apparatus in semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The lens barrel structure comprises a plurality of lens barrels and a plurality of support structures. Each lens barrel has an optical axis. The plurality of optical axes have a parallel orientation. The support structures are parallel to each other and perpendicular to the optical axes of the lens barrels. The support structures maintain the parallel orientation of the lens barrels. The support structures may comprise a first pair of connecting rods for supporting lower portions of the lens barrels, and a second pair of connecting rods for supporting upper portions of the lens barrels. Alternatively, the Support structure may comprise a first support plate for supporting lower portions of the lens barrels, and a second support plate for supporting upper portions of the lens barrels. The support structures are made of a material having a low coefficient of thermal expansion.
The present invention is also directed to a lithography system comprising a lens barrel structure such as for use in a semiconductor manufacturing.
The present invention is further directed to a method for making a lens barrel structure, which, in one embodiment, is used in projection exposure apparatus in a semiconductor manufacturing to reduce a pattern on a reticle through the projection exposure apparatus to a semiconductor wafer. The method comprises the steps of disposing a plurality of lens barrels in a parallel orientation, and providing a plurality of support structures for maintaining the parallel orientation of the lens barrels.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The advantages and purposes may be obtained by means of the combinations set forth in the attached claims.